a recent 'Ask Umbra' column on Grist, there are three factors affecting nutrient loss when you cook vegetables: temperature, time, and water. "Nutrients tend to be both heat-intolerant and water-soluble," the article says, which means that any method that requires a) cooking at a high temperature for a long time, and b) uses a lot of water will result in the greatest nutrient loss. (So by this measure, boiling vegetables is likely the worst offender.) It goes without saying then that cooking at a lower temperature for a shorter amount of time and with less water would result in the least amount of nutrients lost, and that's what the microwave accomplishes. So where did this idea originate in the first place? According to Grist, in 2003 a study from Spain claimed that steaming broccoli in the microwave caused it to lose 97 percent of its antioxidants, while stovetop cooking only resulted in an 11 percent loss. But critics say the study used more water than would ever be necessary in a microwave, and thus the results were flawed. Basically, water, not the microwave, is the most important factor when cooking vegetables, according to Grist. The less water, the better:
Steaming, for instance, is a fairly good option because the veggies have less contact with water. Even better: Cook your veggies in a stew or soup, and you'll be able to slurp those escapee nutrients up. Stovetop stir-frying or sautéing is also a good choice, assuming you don't go crazy with the oil. Baking and roasting are yummy, but don't forget that long exposures to heat will zap some of the nutrients...Of course, other arguments against microwaves have to do with magnetrons and radiation levels, etc., which is a whole other topic. But as far as nutrient loss goes, if microwaving is your preferred choice for cooking vegetables, than cook on. Just watch the amount of water you use!
Read More: Ask Umbra: Does microwaving vegetables zap their nutritional value? | GristRelated: How To Steam Broccoli in the Microwave (Image: Faith Durand)